Modified polyvinyl acetal resin, curable resin composition containing the same, and laminated products

ABSTRACT

Disclosed are a modified polyvinyl acetal resin consisting essentially of repeating units represented by the following formula (I), and a modifier for curable resins which comprises the modified polyvinyl acetal resin:                    
     wherein R 1  represents an optionally substituted aryl group, an optionally substituted aralkyl group, or an optionally substituted alkenyl group having an optionally substituted aryl group; R 2  represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms; R 3  represents an optionally substituted, bivalent hydrocarbon group having 1 to 20 carbon atoms; and a, b, c, d, and e indicate the proportions in mol % of the respective structural units in the formula and satisfy 0&lt;a≦85, 0≦b≦80, 0≦c≦50, 0≦d≦30, and 0&lt;e≦50; a curable resin composition comprising a curable resin (A), a curing agent (B), and a modified polyvinyl acetal resin (C) consisting essentially of repeating units represented by (I′); and a laminated product comprising a layer of the curable resin composition and/or a cured composition obtained therefrom and a substrate layer:                    
     wherein R 1 , R 2 , and R 3  are as defined above and a, b, c, d, and e, indicating the proportions in mol % of the respective structural units in the formula, satisfy 0≦a≦85, 0≦b≦80, 0≦c≦50, 0≦d≦30, 0≦e≦50, and a+b≠0.

This application is a Continuation of application Ser. No. 09/62,321Filed on Jul. 28, 2000.

FIELD OF THE INVENTION

The present invention relates to a modified polyvinyl acetal resin, amodifier for curable resins, a curable resin composition, and laminatedproducts.

The modified polyvinyl acetal resin of the present invention isexcellent not only in dielectric characteristics but in compatibilitywith various solvents and thermosetting resins and in adhesiveness. Theresin is hence useful as an electrical insulating material.

The modifier for curable resins of the invention comprises the specificmodified polyvinyl acetal resin. By adding this modifier to a curableresin, a curable resin composition can be provided which has excellentadhesiveness and is suitable for use as an electrical insulatingmaterial, etc.

The curable resin composition of the invention comprises a curableresin/curing agent combination compounded with a specific modifiedpolyvinyl acetal resin. The composition has greatly improvedfilm-forming properties and can hence be applied to various substratesto form a stable, homogeneous film. Since the film combines excellentadhesiveness to substrates and flexibility, the composition isespecially suitable for use as an adhesive.

The laminated products of the invention comprise a substrate layer and alayer of a curable resin composition containing a specific modifiedpolyvinyl acetal resin and/or of a cured composition obtained by curingthe curable resin composition. Since the layer of the curable resincomposition has greatly improved film-forming properties, it can beapplied to various substrates to form a stable, homogeneous film, whichcombines excellent adhesiveness to the substrates and flexibility. Thelaminated products are hence used especially as adhesives havingexcellent flexibility and high adhesiveness.

BACKGROUND OF THE INVENTION

Curable resins, which mostly comprise low-molecular weight compounds,are applied in the form of a solution in a solvent or in a melt form tosubstrates and then cured under given conditions to thereby exhibitadhesiveness to the substrates. As a result, satisfactory laminatedproducts can be obtained. Furthermore, by superposing an adherend on thesurface of the thus-applied solution or melt of an uncured curable resinand then curing the resin, a three-layer laminated product composed ofthe substrate, an adhesive layer, and the adherend can be obtained inwhich the resin exhibits adhesiveness to the adherend and which also issatisfactory. Besides being used in such applications, curable resinsare extensively used as matrix resins in an application in which fibersor an inorganic or organic filler is mixed with a solution or melt ofthe curable resin and the mixture is cured alone to obtain asatisfactory composite, or in an application in which the mixture islikewise applied to a substrate and united with an adherend.

In the case of using a solid curable resin, a solution prepared bydissolving the resin in a solvent is applied to a substrate and thesolvent which has become unnecessary is removed thereafter to form anexceedingly hard film. However, because the resin has a low-molecularweight, the film is highly brittle and is apt to readily peel off thesubstrate or develop cracks. In the case of using a liquid curableresin, a solution thereof is prepared and applied in the same manner andthe solvent is then removed. In this case, however, there are manyproblems, for example, that the resin, upon solvent removal, returns tothe original liquid state and, as a result, it becomes difficult tomaintain an even film thickness, making it difficult to exhibit even andstable adhesive strength, and that the resin surface has tackiness andthis necessitates significantly complicated operations. Because of thesedrawbacks, a technique is used in which the curing reaction is caused toproceed to some degree to thereby increase the molecular weight of theresin, i.e., bring the resin into the so-called B-stage. Although thistechnique is effective in improving evenness of film thickness, it isdifficult to control the B-stage and to stably maintain the B-stage overlong. In addition, as the molecular weight increases, the ability to wetan adherend decreases, resulting in reduced adhesion strength.Consequently, this technique is not a satisfactory technique forimprovements.

In contrast, an attempt has been made to maintain applicability and filmproperties without increasing the molecular weight of a curable resin asa whole, by adding thereto a rubber, thermoplastic resin, etc. However,curable resins do not always have satisfactory compatibility withrubbers or thermoplastic resins. There are cases where even though thecomposition has been homogenized with a solvent, it undergoes phaseseparation upon solvent volatilization, or undergoes phase separationupon curing reactions after solvent vaporization and coagulates at thecomposition/substrate interface or, conversely, at the composition/airinterface, resulting in an insufficient effect of improvement.

One measure in overcoming the problem described above is proposed, e.g.,in JP-A-5-186667 (the term “JP-A” as used herein means an “unexaminedpublished Japanese patent application”), which is an epoxy resincomposition comprising an epoxy compound, a curing agent, and apolyvinyl acetal resin having a peculiar structure highly compatiblewith the epoxy compound/curing agent combination.

However, this epoxy resin composition was found to have drawbacks thatapplication of the composition to a substrate results in cissing on thesubstrate surface and that curing the applied composition significantlyreduces the flexibility of the substrate.

On the other hand, various insulating materials are known for use in thefield of electronics industry as overcoat materials, interlayerdielectric materials, or the like in semiconductors, ICs, hybrid ICs,wiring circuit boards, display devices, display parts, etc. Examplesthereof include passivation films, soldering resists, plating resists,interlayer dielectric materials, and moisture-proof protective films.These insulating materials also have come to be desired to have higherperformances and higher reliability with the recent trend in electronicparts toward miniaturization, weight reduction, density increase, andspeed increase.

In order for an insulating material to have a smaller dielectric loss,even in a slight degree, it should have a lower dielectric constant anda smaller dielectric loss tangent.

As such materials are used thermosetting resins such as phenolic resins,epoxy resins, and polyimide resins and thermoplastic resins such asfluororesins and polyolefin resins.

However, these thermosetting resins have had difficulties in attaininghigher speeds and higher reliability because they usually have adielectric constant as high as 4.0 or higher and a dielectric losstangent as large as 0.01 or above.

The thermoplastic resins, on the other hand, have had problems, forexample, that they have poor workability, poor adhesiveness, andinsufficient reliability.

SUMMARY OF THE INVENTION

Objects of the invention are (i) to provide a modified polyvinyl acetalresin excellent in dielectric characteristics and in compatibility withthermosetting resins and adhesiveness, (ii) to provide a modifier forcurable resins which has excellent compatibility with curable resins andwhich, when added to a curable resin, improves the dielectriccharacteristics, film-forming properties, and flexibility of the resin,(iii) to provide a curable resin composition in which the modifiedpolyvinyl acetal resin has excellent compatibility with the curableresin and which is excellent in film-forming properties and flexibilityand adhesiveness, and (iv) to provide a laminated product in which astable and even film having excellent adhesiveness to the substrate canbe formed and which has flexibility.

The present inventors made intensive investigations in view of thecircumstances described above. As a result, they have found that (i) amodified polyvinyl acetal resin having a specific structure is excellentnot only in dielectric characteristics but in compatibility with varioussolvents and thermosetting resins and in adhesiveness, (ii) addition ofthis modified polyvinyl acetal resin to a curable resin improves thedielectric characteristics and film-forming properties of the curableresin, (iii) by incorporating a specific modified polyvinyl acetal resinto a combination of a curable resin and a curing agent, a cured resin isobtained which is excellent in film-forming properties, flexibility, andadhesiveness, and (iv) a laminated product comprising a substrate and anadhesive layer comprising a curable resin composition containing themodified polyvinyl acetal resin is excellent in substrate wettabilityand adhesiveness after cure while retaining the intact flexibility ofthe substrate. The present invention has been completed based on thesefindings.

The essential aspects of the present invention reside in a modifiedpolyvinyl acetal resin consisting essentially of repeating unitsrepresented by the following formula (I):

wherein R¹ represents an optionally substituted aryl group, anoptionally substituted aralkyl group, or an optionally substitutedalkenyl group having an optionally substituted aryl group; R² representsa hydrogen atom or an alkyl group having 1 to 10 carbon atoms; R³represents an optionally substituted, bivalent hydrocarbon group having1 to 20 carbon atoms; and a, b, c, d, and e indicate the proportions inmol % of the respective structural units in the formula and satisfy0<a≦85, 0≦b≦80, 0≦c≦50, 0≦d≦30, and 0<e≦50.

In a preferred embodiment of the invention, a modifier for curableresins is provided which comprises the modified polyvinyl acetal resin.

The invention further provides a curable resin composition comprising acurable resin (A) and a curing agent (B) and further containing amodified polyvinyl acetal resin (C) consisting essentially of repeatingunits represented by the following formula (I′), and furthermoreprovides a laminated product comprising a layer of the curable resincomposition and a substrate layer:

wherein R¹ represents an optionally substituted aryl group, anoptionally substituted aralkyl group, or an optionally substitutedalkenyl group having an optionally substituted aryl group; R² representsa hydrogen atom or an alkyl group having 1 to 10 carbon atoms; R³represents an optionally substituted, bivalent hydrocarbon group having1 to 20 carbon atoms; and a, b, c, d, and e indicate the proportions inmol % of the respective structural units in the formula and satisfy0≦a≦85, 0≦b≦80, 0≦c≦50, 0≦d≦30, 0≦e≦50, and a+b≠0.

In this specification, formulae (I) and (I′) are structural formulae,each of which merely indicates the proportions of constituent elementsof the resin, and are not intended to specify an arrangement of theseelements (e.g., a block arrangement). The modified polyvinyl acetalresin represented by formula (I) may contain other constituent elementsas long as these optional elements do not defeat the objects of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be explained below in detail.

(Modified Polyvinyl Acetal Resin)

The characteristic feature of the invention resides in a modifiedpolyvinyl acetal resin consisting essentially of repeating unitsrepresented by formula (I).

In formula (I), R¹ represents an optionally substituted aryl group, anoptionally substituted aralkyl group, or an optionally substitutedalkenyl group having an optionally substituted aryl group; R² representsa hydrogen atom or an alkyl group having 1 to 10 carbon atoms; and R³represents an optionally substituted, bivalent hydrocarbon group having1 to 20 carbon atoms. Furthermore, a, b, c, d, and e indicate theproportions in mol % of the respective structural units in the formulaand satisfy 0≦a≦85, 0≦b80, 0≦c≦50, 0≦d≦30, and 0≦e≦50.

In the case where R¹ in formula (I) is an optionally substituted arylgroup, it preferably has 6 to 12 carbon atoms. Examples thereof includephenyl, tolyl, xylyl, ethylphenyl, methoxyphenyl, aminophenyl,chlorophenyl, and naphthyl.

When R¹ is an optionally substituted aryl group, the resin is improvedin T_(g) and is effective in improving heat resistance.

In the case where R¹ is an optionally substituted aralkyl group, itpreferably has 7 to 12 carbon atoms. Examples thereof include benzyl,phenylethyl, and phenylpropyl.

When R¹ is an optionally substituted aralkyl group, the resin isespecially effective in reducing dielectric loss tangent.

In the case where R¹ is an optionally substituted alkenyl group havingan optionally substituted aryl group, it preferably has 8 to 12 carbonatoms. Examples thereof include phenylvinyl and phenylpropenyl.

R¹ is preferably an optionally substituted aryl group or an optionallysubstituted aralkyl group.

Examples of the substituents of these aryl, aralkyl, and alkenyl groupsinclude alkyl groups such as methyl and ethyl, alkoxy groups such asmethoxy, amino, alkylamino groups, acylamino groups, carboxyl,carboxylic ester groups, hydroxyl group, and halogen atoms such aschloro, besides the substituents given above.

In the case where R² is an alkyl group having 1 to 10, preferably 1 to 8carbon atoms, examples thereof include methyl, ethyl, propyl, butyl, andhexyl.

Preferred examples of R² include methyl and propyl.

R³ is an optionally substituted bivalent hydrocarbon group having 1 to20, preferably 1 to 12 carbon atoms. Examples thereof include methylene,ethylene, trimethylene, butylene, cyclohexylene, methylcyclohexylene,carboxycyclohexylene, norbornylene, vinylene, cyclohexenylene,phenylene, and naphthylene.

Preferred examples of R³ include ethylene, phenylene, and vinylene.

With respect to the proportions (mol %) of the structural units, that ofa is 0≦a≦85, preferably 10≦a≦80; that of b is 0≦b≦80, preferably 0≦b≦70;that of c is 0≦c≦50, preferably 0≦c≦45; that of d is 0≦d≦30, preferably0≦d≦15; and that of e is 0≦e≦50, preferably 1≦e≦50.

In case where a is too small, the resin has an increased dielectricconstant and a lowered T_(g) and is hence less effective inimprovements. In case where c is too large, the resin has enhancedhydrophilicity to show impaired performances due to moisture absorption,has an increased dielectric constant, and is hence less effective inimprovements.

In case where d is too large, the resin has too small a proportion ofacetal groups incorporated through acetalization and hence showsinsufficient performances. In case where e is too small, the resin hasreduced adhesiveness and is less effective in improvements. In casewhere e is too large, the resin has enhanced hydrophilicity to showimpaired performances due to moisture absorption, has an increaseddielectric constant, and is hence less effective in improvements.

In this specification, formula (I) is a structural formula which merelyindicates the proportions of constituent elements of the resin and isnot intended to specify an arrangement of these elements (e.g., a blockarrangement). The modified polyvinyl acetal resin represented by formula(I) may contain other constituent elements as long as these optionalelements do not defeat the objects of the invention.

The modified polyvinyl acetal resin represented by formula (I) generallyhas an acid value of from 5 to 150 mg-KOH/g as determined through thetitration of a solution of 1.0 g of the resin in 200 ml of DMF with 0.5mol/l ethanolic potassium hydroxide solution using automatic titratorGT-05, manufactured by Mitsubishi Chemical Corp.

The modified polyvinyl acetal resin of the invention is suitable for usein electrical insulating materials, and is useful in anisotropicconductive films, interlayer dielectrics, or electronic members forhigh-speed communication apparatus, e.g., routers. On the other hand,the modified polyvinyl acetal resin is applicable to other fields suchas, e.g., adhesives, coating materials, linings, fiber-reinforcedcomposites, and constructional materials so as to take advantage ofproperties thereof such as adhesiveness and film-forming properties.

Since the modified polyvinyl acetal resin is highly compatible, it canbe used in combination with a curable or plastic resin, e.g., an epoxyresin, acrylic resin, or urethane resin.

Inorganic or organic fibers and organic or inorganic fillers may beadded to the composition as long as this addition does not reduce theperformances of the composition.

(Process for Producing Modified Polyvinyl Acetal Resin)

Processes for producing the modified polyvinyl acetal resin of theinvention are not particularly limited. However, a preferred process,for example, comprises acetalizing a polyvinyl alcohol and then reactingthe resultant acetalization product with an acid anhydride to esterifypart of the hydroxyl groups remaining in the acetalization product withthe acid anhydride and thereby modify the acetalization product.

A commercial acetalization product can be used as a starting materialand modified with an acid anhydride.

The acetalization of a polyvinyl alcohol with an aldehyde can beconducted, for example, in accordance with the method described inJP-A-5-140217. An outline of this method is as follows.

The acetalization of a polyvinyl alcohol is accomplished by reacting thepolyvinyl alcohol with an aldehyde represented by formula (II) and/or analdehyde represented by formula (III) with the aid of an acid catalystusually in a solvent.

It is preferred in this case that the water yielded by the reaction bedistilled off as an azeotrope with the solvent.

The polyvinyl alcohol used as a starting material is not particularlylimited, but preferably has a degree of polymerization of from 30 to3,000. Usable examples of commercial polyvinyl alcohol products includeGOHSENOL NL05, manufactured by The Nippon Synthetic Chemical IndustryCo., Ltd.

The aldehydes used as starting materials are respectively represented byformulae (II) and (III):

R¹—CHO  (II)

R²—CHO  (III)

wherein R¹ and R² are the same as in formula (I).

Examples of the aldehyde represented by formula (II) includebenzaldehyde and derivatives thereof, naphthaldehydes and derivativesthereof, cinnamaldehyde and derivatives thereof, and alkylaldehydeshaving a phenyl or naphthyl group. In these aldehydes, the benzene andnaphthalene rings may have one or more substituents selected from alkylgroups, alkoxy groups, amino, alkylamino groups, acylamino groups,carboxyl, carboxylic ester groups, hydroxyl group, and halogen atoms.

Specific examples of these aldehydes include benzaldehyde,1-naphthaldehyde, phenylacetaldehyde, phenylpropionaldehyde,o-tolualdehyde, p-tolualdehyde, o-anisaldehyde, m-anisaldehyde,p-anisaldehyde, p-ethylbenzaldehyde, o-chlorobenzaldehyde,p-chlorobenzaldehyde, and cinnamaldehyde. Preferred of these arebenzaldehyde, phenylacetaldehyde, o-tolualdehyde, and p-tolualdehyde.

The aldehyde represented by formula (II) has an aromatic ring, andincorporation of aromatic rings derived from this aldehyde enables themodified polyvinyl acetal resin to have a reduced dielectric constant, areduced dielectric loss tangent, and an improved T_(g). It can befurther thought that since this modified polyvinyl acetal resin hasimproved compatibility with other resins, it gives, when blended withanother resin, a resin composition having improved viscositycharacteristics and giving a cured composition having improved impactresistance.

Examples of the aldehyde represented by formula (III) includeformaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, caproicaldehyde, caprylaldehyde, and capric aldehyde. Preferred of these areformaldehyde, acetaldehyde, and butyraldehyde.

In the modified polyvinyl acetal resin, a+b is preferably in the rangeof from 30 to 80 mol %.

Further, of the structural units represented by formula (I) of themodified polyvinyl acetal resin, it is preferred that the proportion ofthe structural acetal units having R¹ to the sum of the structuralacetal units having R¹ and the structural acetal units having R², a/a+b,is 10% or more. Too small proportions thereof result in an increaseddielectric constant and a lessened effect in improvements.

As the acid catalyst is used, for example, an inorganic acid such ashydrochloric acid, sulfuric acid, or phosphoric acid, acetic acid, orp-toluenesulfonic acid. Preferred of these are hydrochloric acid,sulfuric acid, and p-toluenesulfonic acid. The use amount of thecatalyst is generally from 0.005 to 0.2 mol per mol of the aldehyde(s).

The solvent is not particularly limited as long as it forms an azeotropewith water and readily separates from the water through liquid/liquidseparation. Preferred examples thereof include aromatic hydrocarbonssuch as benzene, toluene, and xylene. Especially preferred is toluene.

The use amount of the solvent is generally from 100 to 2,000 parts byweight, preferably from 200 to 1,000 parts by weight, per 100 parts byweight of the polyvinyl alcohol used as a starting material.

The reaction temperature is generally from 20 to 90° C., preferably from40 to 70° C. The reaction time is generally from 2 to 10 hours.

The reaction may be conducted either batchwise or continuously.

After completion of the reaction, the target polyvinyl acetal resin canbe recovered from the reaction mixture in an ordinary way. For example,a poor solvent for the target polyvinyl acetal resin, such as methanol,is added to the reaction mixture to precipitate the resin, after thereaction mixture is neutralized and filtered after completion of thereaction. The polyvinyl acetal resin thus precipitated is recovered.According to need, the resin precipitated can be purified by repeatingan operation in which the resin recovered is redissolved in a goodsolvent such as toluene and then precipitated again with the poorsolvent.

Subsequently, the acetalization product obtained is modified with anacid anhydride. This modification can be conducted by using any knownmethod of esterifying an alcohol. More specifically, the modification isconducted by reacting the polyvinyl acetal resin thus obtained with anacid anhydride represented by formula (IV).

The polyvinyl acetal resin obtained by the step described above is usedas a feed material. However, when a commercial product of the resin isavailable, it may be used. The acid anhydride as the other feed materialis one represented by formula (IV):

wherein R³ is the same as in formula (I).

Examples of the acid anhydride represented by formula (IV) includephthalic anhydride, naphthalene-1,2-dicarboxylic anhydride, succinicanhydride, maleic anhydride, glutaric anhydride, trimellitic anhydride,cyclohexane-1,2-dicarboxylic anhydride, 4-cyclohexene-1,2-dicarboxylicanhydride, 4-methylcyclohexane-1,2-dicarboxylic anhydride, andnorbornane-2,3-dicarboxylic anhydride. Preferred of these are phthalicanhydride, succinic anhydride, and maleic anhydride. It is thought thatthe addition of this acid anhydride improves compatibility with otherresins and adhesiveness. Consequently, e in formula (I) is preferably 1mol % or larger.

This reaction may be conducted without using a catalyst. However, byusing a catalyst, the reaction can be carried out under milderconditions. Examples of the catalyst include tertiary amines such aspyridine, lutidine, 4-dimethylaminopyridine, triethylamine,diisopropylethylamine, and N-ethylpiperidine, bases such as sodiumacetate, and acid catalysts such as sulfuric acid, hydrochloric acid,ZnCl₂, and HClO₄. Preferred of these are tertiary amines. The use amountof the catalyst is generally from 0.001 to 1 mol per mol of the acidanhydride.

The reaction can be conducted without using a solvent, i.e., whilekeeping the resin in a bulked state. In the case of using a solvent, thesolvent may be a hydrocarbon, ketone, ester, ether, amide, or anothersolvent. Specific examples thereof include N,N-dimethylformamide,toluene, MEK, and MIBK. The use amount of the solvent is generally from100 to 2,000 parts by weight, preferably from 200 to 1,000 parts byweight, per 100 parts by weight of the polyvinyl acetal resin as a feedmaterial.

The reaction temperature is generally from 30 to 200° C., preferablyfrom 50 to 180° C. The reaction time is generally from 1 to 15 hours.

The reaction may be conducted either batchwise or continuously.

After completion of the reaction, the target modified polyvinyl acetalresin can be recovered from the reaction mixture in an ordinary way. Forexample, a poor solvent for the target modified polyvinyl acetal resin,such as methanol, is added to the reaction mixture to precipitate theresin, after the reaction mixture is neutralized and filtered aftercompletion of the reaction. The modified polyvinyl acetal resin thusprecipitated is recovered. According to need, the resin precipitated canbe purified by repeating an operation in which the resin recovered isredissolved in a good solvent such as acetone and then precipitatedagain with the poor solvent.

(Modifier for Curable Resin)

The modifier for curable resins of the invention is characterized bycomprising the modified polyvinyl acetal resin consisting essentially ofrepeating units represented by formula (I). The modifier may containother ingredients as long as these optional ingredients do not impairthe performances of the modifier. For example, a solvent such as, e.g.,methyl ethyl ketone, may be added for the purpose of mixing timereduction.

The use amount of the modifier for curable resins varies depending onpurposes of the use thereof. However, too small addition amounts interms of the modified polyvinyl acetal resin ingredient result in thereduced ability to form a film on substrates. On the other hand, in casewhere the addition amount thereof is too large, the resultantcomposition has an increased viscosity and hence the solvent volatilizesinsufficiently and partly remains in the film. The residual solvent maybe causative of film blistering or peeling, depending on the subsequentheat history. Consequently, the modified polyvinyl acetal resiningredient represented by formula (I) is added in an amount of generallyfrom 0.1 to 200 parts by weight, preferably from 0.5 to 180 parts byweight, per 100 parts by weight of the curable resin.

(Curable Resin Composition)

The curable resin composition of the invention, which comprises acurable resin (A) and a curing agent (B), is characterized by furthercontaining a modified polyvinyl acetal resin (C) consisting essentiallyof repeating units represented by formula (I′).

Ingredient (C) used in the invention is a modified polyvinyl acetalresin consisting essentially of repeating units represented by formula(I′).

In formula (I′), R¹ represents an optionally substituted aryl group, anoptionally substituted aralkyl group, or an optionally substitutedalkenyl group having an optionally substituted aryl group; R² representsa hydrogen atom or an alkyl group having 1 to 10 carbon atoms; and R³represents an optionally substituted, bivalent hydrocarbon group having1 to 20 carbon atoms. Furthermore, a, b, c, d, and e indicate theproportions in mol % of the respective structural units in the formulaand satisfy 0≦a≦85, 0≦b≦80, 0≦c≦50, 0≦d≦30, 0≦e≦50, and a+b≠0.

In the case where R¹ in formula (I′) is an optionally substituted arylgroup, it preferably has 6 to 12 carbon atoms. Examples thereof includephenyl, tolyl, xylyl, ethylphenyl, methoxypheny, aminophenyl,chlorophenyl, and naphthyl.

When R¹ is an optionally substituted aryl group, the resin is improvedin T_(g) and is effective in improving heat resistance.

In the case where R¹ is an optionally substituted aralkyl group, itpreferably has 7 to 12 carbon atoms. Examples thereof include benzyl,phenylethyl, and phenylpropyl.

When R¹ is an optionally substituted aralkyl group, the resin isespecially effective in reducing dielectric loss tangent.

In the case where R¹ is an optionally substituted alkenyl group havingan optionally substituted aryl group, it preferably has 8 to 12 carbonatoms. Examples thereof include phenylvinyl and phenylpropenyl.

R¹ is preferably an optionally substituted aryl group or an optionallysubstituted aralkyl group.

Examples of the substituents of these aryl, aralkyl, and alkenyl groupsinclude alkyl groups such as methyl and ethyl, alkoxy groups such asmethoxy, amino, alkylamino groups, acylamino groups, carboxyl,carboxylic ester groups, hydroxyl group, and halogen atoms such aschloro, besides the substituents given above.

In the case where R² is an alkyl group having 1 to 10, preferably 1 to 8carbon atoms, examples thereof include methyl, ethyl, propyl, butyl, andhexyl.

Preferred examples of R² include methyl and propyl.

R³ is an optionally substituted bivalent hydrocarbon group having 1 to20, preferably 1 to 12 carbon atoms. Examples thereof include methylene,ethylene, trimethylene, butylene, cyclohexylene, methylcyclohexylene,carboxycyclohexylene, norbornylene, vinylene, cyclohexenylene,phenylene, and naphthylene.

Preferred examples of R³ include ethylene, phenylene, and vinylene.

With respect to the proportions (mol %) of the structural units, that ofa is 0≦a≦85, preferably 0≦a≦80; that of b is 0≦b≦80, preferably 0≦b≦70;the sum of a and b is not equal to 0; that of c is 0≦c≦50, preferably0≦c≦45; that of d is 0≦d≦30, preferably 0≦d≦15; and that of e is 0≦e≦50,preferably 1≦e≦50.

A resin with smaller proportion of the structural acetal units havingR¹, i.e. with smaller a, tends to have an increased dielectric constantand a lowered T_(g). In case where c is too large, the resin hasenhanced hydrophilicity to show impaired performances due to moistureabsorption, has an increased dielectric constant, and is hence lesseffective in improvements.

In case where d is too large, the resin has too small a proportion ofacetal groups incorporated through acetalization and hence showsinsufficient performances. In case where e is too small, the resin hasreduced adhesiveness and is less effective in improvements. In casewhere e is too large, the resin has enhanced hydrophilicity to showimpaired performances due to moisture absorption, has an increaseddielectric constant, and is hence less effective in improvements.

In this specification, formula (I′) is a structural formula which merelyindicates the proportions of constituent elements of the resin and isnot intended to specify an arrangement of these elements (e.g., a blockarrangement). The modified polyvinyl acetal resin represented by formula(I′) may contain other constituent elements as long as these optionalelements do not defeat the objects of the invention.

The use amount of the modified polyvinyl acetal resin of ingredient (C)varies depending on purposes of the use thereof. However, too smalladdition amounts of the modified polyvinyl acetal resin result in thereduced ability to form a film on substrates. On the other hand, in casewhere the addition amount thereof is too large, the resultantcomposition has an increased viscosity and hence the solvent volatilizesinsufficiently and partly remains in the film. The residual solvent maybe causative of film blistering or peeling, depending on the subsequentheat history. Consequently, the incorporation amount of ingredient (C)is generally from 0.1 to 200 parts by weight, preferably from 0.5 to 180parts by weight, per 100 parts by weight of the curable resin.

Provided as a preferred embodiment of the curable resin composition ofthe invention is a curable resin composition which comprises a curableresin (A), a curing agent (B), and a modified polyvinyl acetal resin (C)consisting essentially of repeating units represented by formula (I)wherein a, indicating the proportion of one kind of repeating units inthe resin (C), satisfies 0≦a≦85. When the modified polyvinyl acetalresin is added to a combination of a curable resin and a curing agent,the curable resin composition obtained by mixing these ingredients hasimproved dielectric characteristics irrespective of the kind(s) of thecurable resin and/or the curing agent.

The modified polyvinyl acetal resin has, as an essential component,substituents represented by R¹ which are optionally substituted arylgroups, optionally substituted aralkyl groups, or optionally substitutedalkenyl groups having an optionally substituted aryl group. Anespecially preferred range of the amount of these substituents is suchthat 10≦a≦80. A resin with smaller proportion of the structural acetalunits having R¹, i.e. with smaller a, tends to have an increaseddielectric constant and a lowered T_(g).

Examples of the curable resin of ingredient (A) include epoxy resins,acrylic compounds, isocyanate compounds, and melamine compounds.Preferred of these are epoxy resins from the standpoint of compatibilitywith the modified polyvinyl acetal resin of ingredient (C) and/or of theadhesiveness of the resin composition.

As the epoxy resins can be used various epoxy resins such as, e.g.,bisphenol epoxyes, phenolic novolak epoxyes, cresol novolak epoxyes,glycidylamine epoxyes, alicyclic epoxyes, and glycidyl ester epoxyes.Preferred usable examples of bisphenol A epoxyes include “Epikote” 828,1001, 1004, and 1009 (manufactured by Yuka Shell Epoxy K.K.), “Araldite”GY250 and “Araldite” 6071, 6072, 6097, and 6099 (manufactured byCiba-Geigy Corp.), and “Dow Epoxy” DER 331, 661, 664, and 669(manufactured by The Dow Chemical Co.)

Preferred usable examples of the phenolic novolak epoxyes include“Epikote” 15 and 154 (manufactured by Yuka Shell Epoxy K.K.), “Araldite”EPN 1138 and 1139 (manufactured by Ciba-Geigy Corp.), and “Dow Epoxy”DEN 431, 438, and 485 (manufactured by The Dow Chemical Co.). Preferredusable examples of the cresol novolak epoxyes include “Araldite” ECN1235, 1273, and 1299 (manufactured by Ciba-Geigy Corp.) and “EOCN” 102(manufactured by Nippon Kayaku Co., Ltd.). Preferred usable examples ofthe glycidylamine epoxyes include “Araldite” MY 720 (manufactured byCiba-Geigy Corp.) and “Sumiepoxy” ELM 100, 120, and 434 (manufactured bySumitomo Chemical Co., Ltd.).

Preferred usable examples of the alicyclic epoxyes include “Araldite” CY175, 177, and 179 (manufactured by Ciba-Geigy Corp.). Preferred usableexamples of the glycidyl ester epoxyes include “Epikote” 190P and 191P(manufactured by Yuka Shell Epoxy K.K.) and “Araldite” CY 184 and 192(manufactured by Ciba-Geigy Corp.). Other usable epoxy resins includebisphenol F epoxyes such as “Araldite” XPY 306 (manufactured byCiba-Geigy Corp.) and brominated epoxyes such as “Epikote” 5050 and 5051(manufactured by Yuka Shell Epoxy K.K.).

As the acrylic compounds can be used various acrylic compounds such as,e.g., acrylic or methacrylic esters of mono-or polyhydric alcohols, suchas alkyl acrylates, alkyl methacrylates, and alkylene dimethacrylates,hydroxyl-containing acrylic or methacrylic esters such as hydroxyalkylacrylates and hydroxyalkyl methacrylates, amino-containing acrylic ormethacrylic esters such as aminoalkyl acrylates and aminoalkylmethacrylates, acrylic acid, and methacrylic acid. Specific examples ofthese acrylic compounds include methyl acrylate, ethyl acrylate, propylacrylate, butyl acrylate, isopropyl acrylate, isobutyl acrylate, t-butylacrylate, 2-ethylhexyl acrylate, styryl acrylate, methyl methacrylate,ethyl methacrylate, propyl methacrylate, butyl methacrylate, isopropylmethacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexylmethacrylate, styryl methacrylate, ethylene dimethacrylate,glycidyl-methacrylate, 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate,2-hydroxyethyl methacrylate, 2-aminoethyl acrylate, 2-aminoethylmethacrylate, and acrylic or methacrylic esters produced by causing anyof the epoxy resins enumerated above to add acrylic or methacrylic acid.Basically, any acrylic compound may be used as long as one or moreacrylic or methacrylic groups are present in the chemical molecularstructure thereof.

Usable examples of the isocyanate compounds include toluene2,4-diisocyanate, p-phenylene diisocyanate, and hexamethylenediisocyanate.

As the curing agent of ingredient (B) to be used in the invention isselected a curing agent which enables the curable resin of ingredient(A) to cure sufficiently.

In the case where ingredient (A) is an epoxy resin, usable examples ofingredient (B) include aromatic amines such as m-phenylenediamine,4,4′-methylenedianiline, and diaminodiphenyl sulfone, aliphaticpolyamines such as diethylenetriamine, triethylenetetramine,tetraethylenepentamine, and diethylaminopropylamine, imidazole compoundssuch as 2-ethyl-4-methylimidazole,1-cyanoethyl-2-ethyl-4-methylimidazole, 1-aminoethyl-2-methylimidazole,1-(cyanoethylaminoethyl)-2-methylimidazole, and1-benzyl-2-methylimidazole, acid anhydrides such as maleic anhydride,phthalic anhydride, hexahydrophthalic anhydride, and methylnadicanhydride, phenol compounds, dicyandiamide, and BF₃/amine complexes suchas BF₃/monoethylamine complex and BF₃/piperidine complex.

These curing agents may be used alone or in combination of two or morethereof. A curing accelerator can be suitably used in combination withthe curing agent.

Further, the curing agent is generally used in such an amount that thenumber of active hydrogen atoms contained in, e.g., the amino, imino orphenolic hydroxyl groups derived from the curing agent or the number ofacid anhydride groups of the curing agent is nearly equivalent to thenumber of epoxy groups derived from the epoxy resin.

In the case where ingredient (A) is an acrylic compound, usable examplesof ingredient (B) include peroxides such as benzoyl peroxide and cumenehydroperoxide and diazo compounds such as azobisisobutyronitrile.

Another preferred embodiment of the curable resin composition of theinvention is the curable resin composition described above whichcomprises a curable resin (A), a curing agent (B), and a modifiedpolyvinyl acetal resin (C) consisting essentially of repeating unitsrepresented by formula (I′) and in which the curable resin (A) is anepoxy resin. In this case, when the modified polyvinyl acetal resin (C)is used in combination with an epoxy resin as the curable resin (A), thecurable resin composition obtained by mixing these ingredients isimproved in film-forming properties, flexibility, and adhesivenessirrespective of whether or not the modified polyvinyl acetal resin (C)has, in the structure thereof, groups represented by R¹, i.e.,optionally substituted aryl groups, optionally substituted aralkylgroups, or optionally substituted alkenyl groups having an optionallysubstituted aryl group.

As the epoxy resin in the embodiment shown above can be used variousepoxy resins such as, e.g., bisphenol epoxyes, phenolic novolak epoxyes,cresol novolak epoxyes, glycidylamine epoxyes, alicyclic epoxyes, andglycidyl ester epoxyes. Preferred examples of these types of epoxyesinclude the epoxy compounds enumerated above.

On the other hand, ingredient (B) is, for example, an aromatic amine,alicyclic polyamine, imidazole compound, acid anhydride, phenolcompound, dicyandiamide, or BF₃/amine complex, such as those enumeratedabove.

These curing agents may be used alone or in combination of two or morethereof. A curing accelerator can be suitably used in combination withthe curing agent.

Further, the curing agent is generally used in such an amount that thenumber of active hydrogen atoms contained in, e.g., the amino, imino orphenolic hydroxyl groups derived from the curing agent or the number ofacid anhydride groups of the curing agent is nearly equivalent to thenumber of epoxy groups derived from the epoxy resin.

The resin composition of the invention, which contains the modifiedpolyvinyl acetal resin, is suitable for use in electrical insulatingmaterials, and is useful in anisotropic conductive films, interlayerdielectrics, or electronic members for high-speed communicationapparatus, e.g., routers. On the other hand, the composition isapplicable to other fields such as, e.g., adhesives, coating materials,linings, fiber-reinforced composites, and constructional materials so asto take advantage of properties thereof such as adhesiveness andfilm-forming properties.

Since the composition is highly compatible, it can be used incombination with a curable or plastic resin, e.g., an epoxy resin,acrylic resin, or urethane resin.

Inorganic or organic fibers and organic or inorganic fillers may beadded to the composition as long as this addition does not reduce theperformances of the composition.

Methods for curing the curable resin composition of the invention arenot particularly limited as long as the curable resin can besufficiently cured with the curing agent by the action of heat, light,ultraviolet, etc. When ingredient (A) is an epoxy resin, heating isusually employed. Curing conditions cannot be specified unconditionallybecause they vary depending on the kinds of the epoxy resin and curingagent. However, in the case of a combination of a bisphenol A epoxyresin and an imidazole curing agent, the curing temperature is generallyfrom 10 to 200° C. and the curing time is generally from 1 to 7 hours.

The curable resin composition of the invention may be applied to asubstrate by the so-called wet process after having been mixed using asolvent. Alternatively, the composition may be applied to a substrate bythe so-called hot-melt process after having been mixed without using asolvent optionally with heating. The substrate may be a plastic, metal,ceramic, or another substrate. Examples of the plastic includepolyesters, polyamides, and polyimides. Examples of the metal includealuminum, copper, iron, stainless steel, and silicon. Examples of theceramic include glasses and alumina. Examples of the polyimides amongthese materials include Kapton (trade name; manufactured by TorayIndustries, Inc.) and Upilex (trade name; manufactured by UbeIndustries, Ltd.). Of these, Upilex is especially preferred as thesubstrate.

Although the curable resin composition of the invention is suitable foruse as an adhesive, inorganic or organic fibers or organic or inorganicfillers may be added thereto as long as this addition does not reducethe performances of the composition. The composition is applicable toother fields such as, e.g., coating materials, linings, electricalinsulating materials, and constructional materials so as to takeadvantage of the adhesiveness and film-forming properties thereof.

The curable resin composition of the invention may be applied to asubstrate by the so-called wet process after having been mixed using asolvent, or may be applied to a substrate by the so-called hot-meltprocess after having been mixed without using a solvent optionally withheating. Inorganic or organic fibers or organic or inorganic fillers maybe added to this composition.

The substrate may be a plastic, metal, ceramic, or another substrate.Examples of the plastic include polyesters, polyamides, and polyimides.Examples of the metal include aluminum, copper, iron, stainless steel,and silicon. Examples of the ceramic include glasses and alumina.Examples of the polyimides among these materials include Kapton (tradename; manufactured by Toray Industries, Inc.) and Upilex (trade name;manufactured by Ube Industries, Ltd.). Of these, Upilex is especiallypreferred as the substrate.

(Laminated Product)

The laminated product of the invention comprises a substrate layer and alayer of the curable resin composition containing a modified polyvinylacetal resin represented by formula (I′) and/or a cured compositionobtained by curing the composition.

Examples of processes for producing the laminated product include amethod comprising coating a substrate with either a solution of thecurable resin composition in a solvent or a melt of the composition andthen curing the applied composition under given conditions. Athree-layer laminated product composed of a substrate, an adhesivelayer, and an adherend can be obtained by superposing the adherend onthe surface of the thus-applied solution or melt of the uncured curableresin composition and then curing the composition. Furthermore, whenfibers or an inorganic or organic filler is mixed with a solution ormelt of the curable resin composition and the mixture is likewiseapplied to a substrate, then a laminated product having a curedcomposition united with the adherend can be obtained.

Since the laminated product of the invention has as a component thereofa layer of the curable resin composition and/or of a cured compositionobtained by curing the composition and this layer has improvedfilm-forming properties, there is a wide choice of substrates.Furthermore, since the curable resin composition can form a stable andhomogeneous film having excellent adhesiveness to substrates andflexibility, a highly stable laminated product having especially highflexibility is obtained.

EXAMPLES

The invention will be explained below in more detail by reference toExamples and Comparative Examples. However, the invention should not beconstrued as being limited to these Examples unless the inventiondeparts from the spirit thereof.

The hydroxyl value of each polyvinyl acetal resin obtained wasdetermined in accordance with JIS K6728. The acid value of each modifiedpolyvinyl acetal resin was determined by titrating a solution of 1.0 gof the modified polyvinyl acetal resin in 200 ml of DMF with 0.5 mol/lethanolic potassium hydroxide solution using automatic titrator GT-05,manufactured by Mitsubishi Chemical Corp.

Production Example 1

Production of Polyvinyl Acetal Resin SA

Poly (vinyl acetal) resin SA was produced in the following manner. Intoa 3-liter glass flask were introduced 100 g of a polyvinyl alcohol(trade name, GOHSENOL NL05; manufactured by The Nippon SyntheticChemical Industry Co., Ltd.), 195 g of phenylacetaldehyde, 33 g ofbutyraldehyde, 584 g of toluene, and 13.2 g of 35% hydrochloric acid.The contents were stirred slowly. The flask was set on an oil bath andthe contents were heated to 58° C. over 1.5 hours, held at 58° C. for 5hours, and then allowed to cool. At the time when the contents hadcooled to 35° C., 535.6 g of a methanol solution containing 18.26 g ofsodium acetate dissolved therein was gradually added to neutralize thereaction mixture. The white precipitate thus yielded was removed byfiltration through a 5C filter paper.

All the residual contents were introduced into a flask containing 2,380g of methanol, and the resultant mixture was stirred at 40° C. for 30minutes. The liquid was wholly discarded, and 756 g of toluene was addedto the precipitate to dissolve the same. Thereafter, 2,380 g of methanolwas added thereto to cause precipitation again. This purification stepwas conducted twice. The liquid was wholly discarded, and theprecipitate was air-dried and then transferred to an aluminum vat. Thisvat was placed in a vacuum dryer and the precipitate was dried at adegree of vacuum of 5 Torr and a temperature of 50° C. for 12 hours toobtain 165 g of polyvinyl acetal resin SA.

Values of δ for an NMR spectrum are shown below. ¹H-NMR (300 MHz,DMSO-d6) δ7.1-7.4: (s, aromatic H), δ5.0-4.1: (m, hydroxyl H), (methineH in the structure represented by the following formula (1)), and(methine H in the structure represented by the following formula (2)),δ4.1-3.6: (m, methine H in the structure represented by the followingformula (3)), δ3.0-2.6: (s, methylene H in the structure represented bythe following formula (4)), δ2.2-1.1: (m, methylene H other than in themethylene represented by the following formula (4)), δ1.0-0.9: (s,methyl H).

The resin had a hydroxyl value of 99 mg-KOH/g.

Example 1

Production of Modified Polyvinyl Acetal Resin PA1

Into a 3,000-ml glass flask were introduced 100 g of the polyvinylacetal resin SA obtained in Production Example 1, 70.5 g of phthalicanhydride, 1,000 ml of N,N-dimethylformamide, and 5.8 g of4-dimethylaminopyridine. The contents were stirred slowly. The flask wasset on an oil bath and the contents were heated to 100° C. over 30minutes, held at 100° C. for 4 hours, and then allowed to cool. Thisreaction mixture was filtered through a No. 4 filter paper. All theresidual contents were gradually introduced into a beaker containing5,500 ml of methanol, and the resultant mixture was stirred for 30minutes. As a result, a yellowish white precipitate generated. Theliquid was wholly discarded, and 300 ml of acetone was added to theprecipitate to dissolve the same. Thereafter, 2,500 ml of methanol wasadded thereto to cause precipitation, and the liquid was discardedagain. The residual precipitate was air-dried and then transferred to analuminum vat. This vat was placed in a vacuum dryer and the precipitatewas dried at a degree of vacuum of 5 Torr and a temperature of 80° C.for 12 hours to obtain 140 g of modified polyvinyl acetal resin PA1.

This resin had an acid value of 63 mg-KOH/g.

Thus, a polymer represented by formula (I) wherein R¹═CH₂C₆H₅, R²═C₃H₇,R³═—C₆H₄—, a=46, b=28, c=6, d=1, and e=19 was obtained.

Example 2

Production of Modified Polyvinyl Acetal Resin PA2

Into a 3,000-ml glass flask were introduced 100 g of the polyvinylacetal resin SA obtained in Production Example 1, 47.7 g of succinicanhydride, 1,000 ml of N,N-dimethylformamide, and 5.8 g of4-dimethylaminopyridine. The contents were stirred slowly. The flask wasset on an oil bath and the contents were heated to 100° C. over 30minutes, held at 100° C. for 4 hours, and then allowed to cool. To thisreaction mixture was added 800 g of methanol. All the contents weregradually introduced into a vessel containing 15 liter of water, and theresultant mixture was stirred for 30 minutes. As a result, a yellowishwhite precipitate generated. The liquid was wholly discarded, and amixed solvent consisting of 800 g of methanol and 15 liter of water wasadded to the precipitate to wash the same. The liquid was discardedagain. The residual precipitate was air-dried and then transferred to analuminum vat. This vat was placed in a vacuum dryer and the precipitatewas dried at a degree of vacuum of 5 Torr and a temperature of 80° C.for 12 hours to obtain 104 g of modified polyvinyl acetal resin PA2.

This resin had an acid value of 55 mg-KOH/g.

Thus, a polymer represented by formula (I) wherein R¹═CH₂C₆H₅, R²═C₃H₇,R³═—CH₂CH₂—, a=46, b=28, c=10, d=1, and e=15 was obtained.

Production Example 2

Production of Modified Polyvinyl Acetal Resin PB1

Into a 3,000-ml glass flask were introduced 20 g of a polyvinyl butyralresin (trade name, S-LEC B BL-S; manufactured by Sekisui Chemical Co.,Ltd.; hereinafter sometimes referred to as “polyvinyl acetal resin SB”),14.1 g of phthalic anhydride, 200 ml of N,N-dimethylformamide, and 1.16g of 4-dimethylaminopyridine. The contents were stirred slowly. Theflask was set on an oil bath and the contents were heated to 100° C.over 30 minutes, held at 100° C. for 4 hours, and then allowed to cool.All the contents were gradually introduced into a beaker containing 200g of methanol, and 3 liter of water was further added. The resultantmixture was stirred for 30 minutes. As a result, a yellowish whiteprecipitate generated. The liquid was wholly discarded, and theprecipitate was added to a mixed solvent consisting of 200 g of methanoland 2 liter of water to wash the precipitate. The liquid was discardedagain. The residual precipitate was air-dried and then transferred to analuminum vat. This vat was placed in a vacuum dryer and the precipitatewas dried at a degree of vacuum of 5 Torr and a temperature of 80° C.for 12 hours to obtain 24.1 g of modified polyvinyl acetal resin PB1.

This resin had an acid value of 87 mg-KOH/g.

Thus, a polymer represented by formula (I) wherein R² 50 C₃H₇,R³═—C₆H₄—, a=0, b=60, c=16, d=3, and e=21 was obtained.

Production Example 3

Production of Modified Polyvinyl Acetal Resin PB2

Into a 1,000-ml glass flask were introduced 80 g of a polyvinyl butyralresin (trade name, S-LEC B BL-S; manufactured by Sekisui Chemical Co.,Ltd.), 7.1 g of succinic anhydride, and 200 g of N,N-dimethylformamide.The contents were stirred slowly. The flask was set on an oil bath andthe contents were heated to 60° C. over 30 minutes to completelydissolve the same. Subsequently, the solution was heated to 100° C. over30 minutes, held at 100° C. for 4 hours, and then allowed to cool. Allthe contents were gradually dropped into a beaker containing 1,600 g ofwater.

The resultant particulate precipitate was taken out by filtration,washed with 160 g of water, and then transferred to a 3-liter flask.Into this flask were introduced 1,600 g of water and 160 g of methanol.The contents were stirred at 45° C. for 1 hour.

The precipitate was taken out by filtration, washed with 160 g of water,and then transferred to a stainless-steel vat. This precipitate wasdried in a hot-air drying oven at 60° C. for 42 hours and then furtherdried in a vacuum dryer at a degree of vacuum of 5 Torr and atemperature of 70° C. for 119 hours to obtain 83 g of modified polyvinylacetal resin PB2.

This resin had an acid value of 40 mg-KOH/g.

Thus, a polymer represented by formula (I) wherein R²═C₃H₇, R³═—CH₂CH₂—,a=0, b=60, c=29, d=3, and e=8 was obtained.

The compositions of the modified polyvinyl acetal resins PA1, PA2, PB1,and PB2 respectively obtained in Examples 1 and 2 and ProductionExamples 2 and 3 are shown in Table 1 together with the composition ofthe polyvinyl acetal resin SA obtained in Production Example 1 and thatof commercial polyvinyl butyral SB.

TABLE 1 Structures of modified polyvinyl acetal resins and unmodifiedpolyvinyl acetal resins Composition of resin Resin a b c d e Example 1PA1 46 28  6 1 19 Example 2 PA2 46 28 10 1 15 Production Example 2 PB1 0 60 16 3 21 Production Example 3 PB2  0 60 29 3  8 Production Example1 SA 46 28 25 1  0 Polyvinyl butyral SB  0 60 37 3  0 Symbols a, b, c,d, and e indicate the proportions (mol %) of the respective structuralunits in formula (I).

Symbols a, b, c, d, and e indicate the proportions (mol %) of therespective structural units in formula (I).

R¹═CH₂C₆H₅, R²═C₃H⁷, R³═—C₆H₄— (Example 1 and Production Example 2) or—CH₂CH₂— (Example 2 and Production Example 3).

Production Example 4

Production of Polyvinyl Acetal Resin SC

Poly (vinyl acetal) resin SC was produced in the following manner. Intoa 3-liter glass flask were introduced 200 g of a polyvinyl alcohol(trade name, GOHSENOL NL05; manufactured by The Nippon SyntheticChemical Industry Co., Ltd.), 336 g of benzaldehyde, 66 g ofbutyraldehyde, 1,163 g of toluene, and 10.56 g of 35% hydrochloric acid.The contents were stirred slowly. The flask was set on an oil bath andthe contents were heated to 75° C. over 0.75 hour and then held at 75°C. for 2 hours. Thereafter, 31.68 g of 35% hydrochloric acid was addedthereto, and this mixture was held for 5 hours and then allowed to cool.At the time when the mixture had cooled to 35° C., 600 g of a methanolsolution containing 52.7 g of sodium acetate dissolved therein wasgradually added to neutralize the reaction mixture. This reactionmixture was poured into 3,500 g of methanol with stirring, and theresultant precipitate was dissolved in 1,200 g of toluene. A 1,120 gportion of this solution was filtered through a 5C filter paper. Thefiltrate was poured into 2,100 g of methanol with stirring to obtain438.4 g of a precipitate. This precipitate was transferred to a 3-literseparable flask, and 350 g of toluene was added thereto to dissolve theprecipitate with heating at 60° C. To this solution was gradually added1,200 g of methanol to cause precipitation. This purification step wasconducted twice. The liquid was discarded, and the precipitate wasair-dried, transferred to a vacuum dryer, and dried therein at a degreeof vacuum of 5 Torr and a temperature of 80° C. for 36 hours to obtain213.2 g of polyvinyl acetal resin SC.

Values of δ for an NMR spectrum are shown below.

¹H-NMR (300 MHz, DMSO-d6) δ7.5-7.2: (d, aromatic H), δ5.9-5.4: (d,methine H in the structure represented by formula (5)), δ5.0-3.6: (m,hydroxyl H), (s, methine H in the structure represented by formula (1)),and (d, methine H in the structure represented by formula (3)),δ2.2-1.1: (m, methylene H), δ1.0-0.8: (s, methyl H).

The resin had a hydroxyl value of 96 mg-KOH/g.

Example 3

Production of Modified Polyvinyl Acetal Resin PC1

Into a 3,000-ml glass flask were introduced 200 g of the polyvinylacetal resin SC obtained in Production Example 4, 85.2 g of succinicanhydride, and 500 g of N,N-dimethylformamide. The contents were stirredslowly. The flask was set on an oil bath and the contents were held at80° C. for 1.5 hours to completely dissolve the same. Thereafter, 11.6 gof 4-dimethylaminopyridine was added to the solution, and this mixturewas held at 100° C. for 4 hours and then allowed to cool. Thereto wasadded 200 g of N,N-dimethylformamide. All the contents were graduallydropped into a beaker containing 8,000 ml of water. The solid obtainedwas taken out by filtration, placed in a beaker containing 2,100 g ofmethanol, allowed to stand for 10 hours, and then taken out byfiltration. This operation was conducted twice. The solid recovered wasdissolved in 250 g of acetone, and 1,200 g of methanol was addedthereto. As a result, a brown precipitate was obtained. The liquid wasdiscarded, and 250 g of acetone was added to the precipitate to dissolvethe same. Thereafter, 400 g of methanol was added thereto to obtain aprecipitate, and the liquid was discarded. The residual precipitate wasadded to 1,100 g of water, and this mixture was treated with a mixer forpulverization. The pulverized precipitate was taken out by filtration,transferred to a vacuum dryer, and dried therein at a degree of vacuumof 5 Torr and a temperature of 80° C. for 55 hours to obtain 209 g ofmodified polyvinyl acetal resin PC1.

This resin had an acid value of 67.8 mg-KOH/g.

Thus, a polymer represented by formula (I) wherein R¹═C₆H₅, R²═C₃H₇,R₃═—CH₂CH₂ —, a=41, b=35, c=5, d=1, and e=18 was obtained.

Production Example 5

Production of Polyvinyl Acetal Resin SD

Polyvinyl acetal resin SD was produced in the following manner. Into a1-liter glass flask were introduced 40 g of a polyvinyl alcohol (tradename, GOHSENOL NL05; manufactured by The Nippon Synthetic ChemicalIndustry Co., Ltd.), 99 g of 1-naphthaldehyde, 13 g of butyraldehyde,234 g of toluene, and 8.5 g of 35% hydrochloric acid. The contents werestirred slowly. The flask was set on an oil bath and the contents wereheated to 75° C. over 0.75 hour, held at 75° C. for 5 hours, and thenallowed to cool. At the time when the contents had cooled to 40° C., 250g of methanol was added thereto. As a result, a brown precipitategenerated. The liquid was discarded, and 100 g of toluene was added tothe precipitate. This mixture was heated to 60° C. with stirring.

Fifty grams of a methanol solution containing 10.5 g of sodium acetatedissolved therein was gradually added to the mixture to neutralize thesame. To this reaction mixture was added 200 g of methanol withstirring. The precipitate obtained was dissolved in 120 g of toluene,and 300 g of methanol was added to the solution to cause precipitationagain. This operation was conducted three times.

The liquid was discarded, and the precipitate was air-dried, transferredto a vacuum dryer, and dried therein at a degree of vacuum of 5 Torr anda temperature of 80° C. for 72 hours to obtain 35 g of polyvinyl acetalresin SD.

Values of 6 for an NMR spectrum are shown below. ¹H-NMR (300 MHz, CDCl₃)δ7.1-8.3: (m, aromatic H), δ5.9-6.5: (m, methine H in the structurerepresented by formula (5)), δ3.4-5.3: (m, hydroxyl H), (methine H inthe structure represented by formula (1)), and (methine H in thestructure represented by formula (3)), δ1.0-2.7: (m, methylene H),δ0.6-1.0: (s, methyl H).

The resin had a hydroxyl value of 155.6 mg-KOH/g.

Example 4

Production of Modified Polyvinyl Acetal Resin PD1

Into a 500-ml glass flask were introduced 20 g of the polyvinyl acetalresin SD obtained in Production Example 5, 8.5 g of succinic anhydride,and 50 g of N,N-dimethylformamide. The contents were stirred slowly. Theflask was set on an oil bath and the contents were held at 80° C. for1.5 hours. Thereafter, this mixture was held at 100° C. for 4 hours andthen allowed to cool. Thereto was added 50 g of N,N-dimethylformamide.All the contents were gradually dropped into a beaker containing 1400 mlof water. The solid obtained was taken out by filtration and dissolvedin 100 g of methyl ethyl ketone, and 200 g of methanol was addedthereto. As a result, a brown precipitate was obtained. The liquid wasdiscarded, and 150 g of methyl ethyl ketone and 100 g of toluene wereadded to the precipitate to dissolve the same. This mixture was filteredthrough a 5C filter paper. Thereafter, 200 g of methanol was addedthereto to obtain a precipitate, and the liquid was discarded. Theprecipitate was transferred to a vacuum dryer, and dried therein at adegree of vacuum of 5 Torr and a temperature of 80° C. for 55 hours toobtain 14.5 g of modified polyvinyl acetal resin PD1.

This resin had an acid value of 70.1 mg-KOH/g.

Thus, a polymer represented by formula (I) wherein R¹═C₁₀H₇, R²═C₃H₇,R²═—CH₂CH₂—, a=35, b=27, c=18, d=1, and e=19 was obtained.

Production Example 6

Production of Polyvinyl Acetal Resin SE

Poly (vinyl acetal) resin SE was produced in the following manner. Intoa 1-liter glass flask were introduced 40 g of a polyvinyl alcohol (tradename, GOHSENOL NL05; manufactured by The Nippon Synthetic ChemicalIndustry Co., Ltd.), 85 g of phenylpropionaldehyde, 13 g ofbutyraldehyde, 234 g of toluene, and 8.45 g of 35% hydrochloric acid.The contents were stirred slowly. The flask was set on an oil bath andthe contents were heated to 75° C. over 0.75 hour, held at 75° C. for 5hours, and then allowed to cool. At the time when the contents hadcooled to 35° C., 150 g of a methanol solution containing 10.6 g ofsodium acetate dissolved therein was gradually added to neutralize thereaction mixture. This reaction mixture was filtered through a 5C filterpaper.

Into the filtrate was poured 800 g of methanol with stirring. As aresult, a light-yellow precipitate generated. The liquid was discarded,and the precipitate was dissolved in 300 g of toluene. To this solutionwas added 800 g of methanol to cause precipitation again. This operationwas conducted three times.

The liquid was discarded, and the precipitate was air-dried, transferredto a vacuum dryer, and dried therein at a degree of vacuum of 5 Torr anda temperature of 80° C. for 72 hours to obtain 31.9 g of polyvinylacetal resin SE.

Values of δ for an NMR spectrum are shown below. ¹H-NMR (300 MHz,DMSO-d6) δ7.0-7.6: (d, aromatic H), δ3.5-5.0: (m, hydroxyl H), (methineH in the structure represented by formula (1)), (methine H in thestructure represented by formula (2)), and (methine H in the structurerepresented by formula (3)), δ1.2-3.0: (m, methylene H in the structurerepresented by formula (4)), (m, methylene H other than in the methylenerepresented by formula (4)), δ0.8-1.1: (s, methyl H).

The resin had a hydroxyl value of 72.8 mg-KOH/g.

Example 5

Production of Modified Polyvinyl Acetal Resin PE1

Into a 500-ml glass flask were introduced 20 g of the polyvinyl acetalresin SE obtained in Production Example 6, 8.5 g of succinic anhydride,and 50 g of N,N-dimethylformamide. The contents were stirred slowly. Theflask was set on an oil bath and the contents were held at 80° C. for1.5 hours to completely dissolve the same. Thereafter, 1.2 g of4-dimethylaminopyridine was added thereto, and this mixture was held at100° C. for 4 hours and then allowed to cool. Thereto was added 50 g ofN,N-dimethylformamide. Thereafter, 200 g of methanol was added theretoto obtain a precipitate, and the liquid was discarded. The precipitatewas dissolved in 50 g of toluene, and 200 g of methanol was added tothis solution to cause precipitation again, and the liquid wasdiscarded. This operation was conducted three times. The precipitate wastransferred to a vacuum dryer, and dried therein at a degree of vacuumof 5 Torr and a temperature of 80° C. for 55 hours to obtain 21.1 g ofmodified polyvinyl acetal resin PE1.

This resin had an acid value of 42.3 mg-KOH/g.

Thus, a polymer represented by formula (I) wherein R¹═C₂H₄Ph, R²═C₃H₇,R³═—CH₂CH₂—, a=59, b=19, c=8, d=1, and e=13 was

The compositions of the modified polyvinyl acetal resins PC1, PD1, andPE1 respectively obtained in Examples 3 to 5 are shown in Table 2together with the compositions of the polyvinyl acetal resins SC, SD,and SE respectively obtained in Production Examples 4 to 6.

TABLE 2 Structures of modified polyvinyl acetal resins and unmodifiedpolyvinyl acetal resins Composition of resin Resin a b c d e Example 3PC1 41 35  5 1 18 Example 4 PD1 35 27 18 1 19 Example 5 PE1 59 19  8 113 Production Example 4 SC 41 35 23 1  0 Production Example 5 SD 35 2737 1  0 Production Example 6 SE 59 19 21 1  0 Symbols a, b, c, d, and eindicate the proportions (mol %) of the respective structural units informula (I).

Symbols a, b, c, d, and e indicate the proportions (mol %) of therespective structural units in formula (I).

R¹═C₆H₅ (Example 3 (PC1)), Production Example 4 (SC)), C₁₀H₇ (Example 4(PD1), Production Example 5 (SD)), or C₂H₄Ph (Example (PE1), ProductionExample 6 (SE)), R²═C₃H₇, R³═—CH₂CH₂—.

Example 6

In 24.0 g of methyl ethyl ketone was dissolved 6.0 g of the modifiedpolyvinyl acetal resin PA1. This solution was applied to a polyethylenesheet with a 10-mil applicator, and the coating was dried at 60° C. for1 hour. Subsequently, the coated sheet was placed in a vacuum dryer anddried therein at a degree of vacuum of 5 Torr and a temperature of 60°C. for 12 hours. The polyethylene sheet was peeled off to obtain a filmyresin. This resin was examined for dielectric constant and dielectricloss tangent at 10 MHz using an impedance analyzer (HP4291A,manufactured by HEWLETT-PACKARD Co.).

Example 7

The same experiment as in Example 6 was conducted, except that modifiedpolyvinyl acetal resin PA2 was used in place of PA1.

Example 8

The same experiment as in Example 6 was conducted, except that modifiedpolyvinyl acetal resin PC1 was used in place of PA1.

Example 9

The same experiment as in Example 6 was conducted, except that modifiedpolyvinyl acetal resin PD1 was used in place of PA1.

Example 10

The same experiment as in Example 6 was conducted, except that modifiedpolyvinyl acetal resin PE1 was used in place of PA1.

Comparative Example 1

The same experiment as in Example 6 was conducted, except that modifiedpolyvinyl acetal resin PB1 was used in place of PA1.

Comparative Example 2

The same experiment as in Example 6 was conducted, except that polyvinylbutyral resin SB (trade name, S-LEC B BL-S; manufactured by SekisuiChemical Co., Ltd.) was used in place of modified polyvinyl acetal resinPA1.

Comparative Example 3

The same experiment as in Example 6 was conducted, except that modifiedpolyvinyl acetal resin PB2 was used in place of PA1.

In Table 3 are shown the results obtained in Examples 6 to 10 andComparative Examples 1 to 3.

The results show that resins PB1 and PB2, corresponding to a=0, andpolyvinyl butyral resin SB had larger dielectric loss tangents than PA1,PA2, PC1, PD1 and PES, used in Examples 6 to 10.

TABLE 3 Dielectric constants and dielectric loss tangents of modifiedpolyvinyl acetal resins ε tan δ Film Resin (10 MHZ) (×10E−3) thicknessExample 6 PA1 2.0 5.8 25 Example 7 PA2 2.1 5.8 26 Example 8 PC1 2.1 9.028 Example 9 PD1 2.0 6.4 25 Example 10 PE1 2.0 5.4 26 Comparative PB12.1 9.6 26 Example 1 Comparative PB2 2.1 11.4 28 Example 3 ComparativePolyvinyl 2.1 10.7 25 Example 2 butyral resin SB

Example 11

In 9.0 g of methyl ethyl ketone were dissolved 1.2 g of an epoxy resin(Epikote 828, manufactured by Yuka Shell Epoxy K.K.), 0.036 g of1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, and 1.8 g of modifiedpolyvinyl acetal resin PA1 to obtain resin composition CA1. Thiscomposition was applied to a polyimide film (Upilex R, manufactured byUbe Industries, Ltd.) with an applicator having a gap of 10 mils. Thecoating was air-dried and then dried in a hot-air drying oven at 180° C.for 2 hours to cure the resin. The coating film obtained was subjectedto a crosscut cellophane tape peeling test in accordance with JIS K5400, in which the coating film was crosshatch-wise incised at aninterval of 1 mm to make 10×10 squares. The number of remaining squareswas counted to judge the adhesiveness of the coating film. The film hada satisfactory appearance. As a result of the cellophane tape peelingtest, no squares peeled off.

Example 12

The same experiment as in Example 11 was conducted, except that modifiedpolyvinyl acetal resin PA2 was used in place of PA1 used in Example 11.Thus, resin composition CA2 was obtained. This resin composition wasevaluated for adhesiveness. It had a satisfactory appearance. As aresult of the cellophane tape peeling test, no squares peeled off.

Example 13

The same experiment as in Example 11 was conducted, except that modifiedpolyvinyl acetal resin PB1 was used in place of PA1 used in Example 11.Thus, resin composition CB1 was obtained. This resin composition wasevaluated for adhesiveness. It had a satisfactory appearance. As aresult of the cellophane tape peeling test, no squares peeled off.

Example 14

The same experiment as in Example 11 was conducted, except that modifiedpolyvinyl acetal resin PB2 was used in place of PA1 used in Example 11.Thus, resin composition CB2 was obtained. This resin composition wasevaluated for adhesiveness. It had a satisfactory appearance. As aresult of the cellophane tape peeling test, no squares peeled off.

Example 15

The same experiment as in Example 11 was conducted, except that modifiedpolyvinyl acetal resin PC1 was used in place of PA1 used in Example 11.Thus, resin composition CC1 was obtained. This resin composition wasevaluated for adhesiveness. It had a satisfactory appearance. As aresult of the cellophane tape peeling test, no squares peeled off.

Example 16

The same experiment as in Example 11 was conducted, except that modifiedpolyvinyl acetal resin PD1 was used in place of PA1 used in Example 11.Thus, resin composition CD1 was obtained. This resin composition wasevaluated for adhesiveness. It had a satisfactory appearance. As aresult of the cellophane tape peeling test, no squares peeled off.

Example 17

The same experiment as in Example 11 was conducted, except that modifiedpolyvinyl acetal resin PE1 was used in place of PA1 used in Example 11.Thus, resin composition CE1 was obtained. This resin composition wasevaluated for adhesiveness. It had a satisfactory appearance. As aresult of the cellophane tape peeling test, no squares peeled off.

Comparative Example 4

The same experiment as in Example 11 was conducted, except that SA wasused in place of modified polyvinyl acetal resin PA1 used in Example 11.Thus, resin composition CSA was obtained. This resin composition wasevaluated for adhesiveness.

In the crosscut cellophane tape peeling test, all the 10×10 squarespeeled off.

Comparative Example 5

The same experiment as in Example 11 was conducted, except thatpolyvinyl butyral resin SB (trade name, S-LEC B BL-S; manufactured bySekisui Chemical Co., Ltd.) was used in place of modified polyvinylacetal resin PA1 used in Example 11. Thus, resin composition CSB wasobtained. This resin composition was evaluated for adhesiveness.

In the crosscut cellophane tape peeling test, all the 10×10 squarespeeled off.

Comparative Example 6

In 9.0 g of methyl ethyl ketone were dissolved 1.2 g of an acrylic resin(BR-80, manufactured by Mitsubishi Rayon Co., Ltd.) and 1.8 g of theabove modified polyvinyl acetal resin PB2 to obtain resin compositionCB2m. This resin composition was evaluated for adhesiveness.

It had fine unevenness and white turbidity. In the crosscut cellophanetape peeling test, all the 10×10 squares peeled off.

The results obtained in Examples 11 to 17 and Comparative Examples 4 to6 are shown in Table 4.

The results show that CA1, CA2, CB1, CB2, CC1, CD1, and CE1, which eachhad carboxylic functional groups, gave resin compositions having betteradhesiveness than those obtained from CSA and CSB, which each had nosuch functional groups. Further, CB2m which is a mixture of a modifiedpolyvinyl acetal resin and an acrylic resin was poor in both appearanceand adhesiveness.

TABLE 4 Adhesiveness of mixtures with epoxy Resin Cellophane compositionResin Appearance tape peeling Example 11 CA1 PA1 good good (no peeling)Example 12 CA2 PA2 good good (no peeling) Example 13 CB1 PB1 good good(no peeling) Example 14 CB2 PB2 good good (no peeling) Example 15 CC1PC1 good good (no peeling) Example 16 CD1 PD1 good good (no peeling)Example 17 CE1 PE1 good good (no peeling) Comparative CSA SA good N.G.(wholly Example 4 peeled off) Comparative CSB SB good N.G. (whollyExample 5 (polyvinyl peeled off) butyral) Comparative CB2m PB2 N.G. N.G.(wholly Example 6 peeled off)

Example 18

In 40 g of methyl ethyl ketone were dissolved 16.0 g of an epoxy resin(Epikote 828, manufactured by Yuka Shell Epoxy K.K.), 0.48 g of1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, and 4. 0 g of modifiedpolyvinyl acetal resin PA1 to obtain resin composition CA1′.

Example 19

The same procedure as in Example 18 was conducted, except that PA2 wasused in place of the modified polyvinyl acetal resin. Thus, compositionCA2′ was obtained.

Example 20

The same procedure as in Example 18 was conducted, except that PB1 wasused in place of the modified polyvinyl acetal resin. Thus compositionCB1′ was obtained.

Example 21

In 32.5 g of methyl ethyl ketone were dissolved 19.0 g of an epoxy resin(Epikote 828, manufactured by Yuka Shell Epoxy K.K.), 0.57 g of1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, and 1.0 g of modifiedpolyvinyl acetal resin PA1 to obtain resin composition CA1″.

Example 22

In 90 g of methyl ethyl ketone were dissolved 12.0 g of an epoxy resin(Epikote 828, manufactured by Yuka Shell Epoxy K.K.), 0.36 g of1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, and 18.0 g of modifiedpolyvinyl acetal resin PA1 to obtain resin composition CA1′.

Comparative Example 7

In 24 g of methyl ethyl ketone were dissolved 16.0 g of an epoxy resin(Epikote 828, manufactured by Yuka Shell Epoxy K.K.) and 0.48 g of1-(2-cyanoethyl)-2-ethyl-4-methylimidazole to obtain resin compositionCX.

Comparative Example 8

In 40 g of methyl ethyl ketone were dissolved 16.0 g of an epoxy resin(Epikote 828, manufactured by Yuka Shell Epoxy K.K.), 0.48 g of1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, and 4.0 g of polyvinylacetal resin SA to obtain resin composition CSA′.

The makeups of the compositions are shown in Table 5.

TABLE 5 Composition Curable Curing obtained resin agent Other additiveExample 18 CA1′ Epikote 2E4MZCN modified 828 (16.0) (0.48) polyvinylacetal resin PA 1 (4.0) Example 19 CA2′ Epikote 2E4MZCN modified 828(16.0) (0.48) polyvinyl acetal resin PA 2 (4.0) Example 20 CB1′ Epikote2E4MZCN modified 828 (16.0) (0.48) polyvinyl acetal resin PB 1 (4.0)Example 21 CA1″ Epikote 2E4MZCN modified 828 (19.0) (0.57) polyvinylacetal resin PA 1 (1.0) Example 22 CA1′′′ Epikote 2E4MZCN modified 828(12.0) (0.36) polyvinyl acetal resin PA 1 (18.0) Comparative CX Epikote2E4MZCN none Example 7 828 (16.0) (0.48) Comparative CSA′ Epikote2E4MZCN polyvinyl acetal Example 8 828 (16.0) (0.48) resin SA (4.0)Epikote 828 is an epoxy resin manufactured by Yuka Shell Epoxy K.K.2E4MZCN is 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole. The numeral ineach parenthesis indicates the incorporation amount (g).

Epikote 828 is an epoxy resin manufactured by Yuka Shell Epoxy K.K.

2E4MZCN is 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole. The numeral ineach parenthesis indicates the incorporation amount (g).

Examples 23 to 27 and Comparative Examples 9 and 10

Each of the compositions (solutions) obtained in Examples 18 to 22 andComparative Examples 7 and 8 was applied to a polyimide film (Upilex R,manufactured by Ube Industries, Ltd.) with an applicator having a gap of10 mils. The coating was air-dried and then heated in a hot-air dryingoven at 180° C. for 2 hours to cure the resin. Thus, laminated productswere obtained. These laminated products were examined for appearance andsubjected to a flexibility test. In the flexibility test, each laminatedproduct was pressed against a 3-φ stainless-steel rod in such a mannerthat the back side of the laminated product came into contact with therod, and the cured composition was visually evaluated for anyabnormality. The results obtained are shown in Table 6.

Table 6 shows that when a modified polyvinyl acetal resin represented byformula (I′) was not used and when polyvinyl acetal resin SA was used inplace of a modified polyvinyl acetal resin represented by formula (I′),then the coating film obviously had a poor appearance.

TABLE 6 Results of flexibility test Appearance (after FlexibilityComposition cure) test Example 23 CA1′ good good Example 24 CA2′ goodgood Example 25 CB1′ good good Example 26 CA1″ good good Example 27CA1′′′ good good Comparative CX poor (considerable good Example 9unevenness of thickness) Comparative CSA′ poor (substrate — Example 10surface was exposed)

Examples 28 to 32 and Comparative Examples 11 and 12

Each of the compositions (solutions) obtained in Examples 18 to 22 andComparative Examples 7 and 8 was applied to an aluminum film with anapplicator having a gap of 25 mils. The coating was air-dried and thenheated in a hot-air drying oven at 180° C. for 2 hours to cure theresin. Thus, laminated products were obtained. These laminated productswere examined for appearance and subjected to a crosscut cellophane tapepeeling test. In the crosscut cellophane tape peeling test, the coatingside was crosshatch-wise incised with a cutter at an interval of 1 mm tomake 10×10 squares, and a cellophane tape was tightly applied to theincised surface and then stripped at a breath. Whether the squares werepeeled off or not was visually evaluated. The results obtained are shownin Table 7.

Table 7 shows that when a modified polyvinyl acetal resin represented byformula (I′) was not used and when polyvinyl acetal resin SA was used inplace of a modified polyvinyl acetal resin represented by formula (I′),then the coating layer obviously had poor adhesiveness.

TABLE 7 Results of adhesiveness test Appearance Adhesiveness inComposition (after cure) peeling test Example 28 CA1′ good good Example29 CA2′ good good Example 30 CB1′ good good Example 31 CA1″ good goodExample 32 CA1′′′ good good Comparative CX good wholly peeled Example 11off Comparative CSA′ good wholly peeled Example 12 off

Example 33

In 24.0 g of methyl ethyl ketone was dissolved 6.0 g of modifiedpolyvinyl acetal resin PC1. This solution was applied to a polyethylenesheet with a 10-mil applicator, and the coating was dried at 60° C. for0.5 hours. After the coated sheet was allowed to cool, the solution wasapplied again to the coating film with a 10-mil applicator and dried at60° C. for 1 hour. Subsequently, this coated sheet was transferred to avacuum dryer and dried therein at a degree of vacuum of 5 Torr and atemperature of 60° C. for 12 hours. The polyethylene sheet was peeledoff to obtain a filmy resin.

This resin was cut into strips having a width of 4 mm, which wereanalyzed with TMA 120 (manufactured by Seiko Instruments Inc.) under aload of 5 g at a heating rate of 2° C./min to determine the glasstransition temperature thereof.

Example 34

The same experiment as in Example 33 was conducted, except that modifiedpolyvinyl acetal resin PA2 was used in place of PC1.

Example 35

The same experiment as in Example 33 was conducted, except that modifiedpolyvinyl acetal resin PD1 was used in place of PC1.

Example 36

The same experiment as in Example 33 was conducted, except that modifiedpolyvinyl acetal resin PE1 was used in place of PC1.

Comparative Example 13

The same experiment as in Example 33 was conducted, except that modifiedpolyvinyl acetal resin PB2 was used in place of PC1.

The results obtained in Examples 33 to 36 and Comparative Example 13 areshown in Table 8.

Table 8 shows that resins PA2, PC1, PD1, and PE1, each corresponding toa>0, had higher glass transition temperatures than resin PB2,corresponding to a=0.

TABLE 8 Glass transition temperatures of modified polyvinyl acetalresins Resin T_(g) Example 33 PC1 105.4 Example 34 PA2 82.8 Example 35PD1 122.0 Example 36 PE1 66.5 Comparative Example 13 PB2 63.6

Example 37

In 9.0 g of methyl ethyl ketone were dissolved 1.2 g of an epoxy resin(Epikote 828, manufactured by Yuka Shell Epoxy K.K.), 0.036 g of1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, and 1.8 g of modifiedpolyvinyl acetal resin PB2 to obtain resin composition CA11 ″″. Thiscomposition was applied to a Teflon sheet with an applicator having agap of 10 mils, and the coating was dried at 60° C. for 0.5 hour. Afterthe coated sheet was allowed to cool, the composition was applied againto the coating film with a 10-mil applicator, dried at 60° C. for 0.5hour, and then heated in a hot-air drying oven at 180° C. for 2 hours tocure the resin.

The Teflon sheet was peeled off, and the filmy resin obtained wasexamined for dielectric constant and dielectric loss tangent at 10 MHzusing an impedance analyzer (HP4291A, manufactured by HEWLETT-PACKARDCo.)

Example 38

The same procedure as in Example 37 was conducted, except that modifiedpolyvinyl acetal resin PA2 was used in place of PB2. Thus, resincomposition CA2″″ was obtained, which was examined for dielectricconstant and dielectric loss tangent at 10 MHz in the same manner as inExample 37.

Example 39

The same procedure as in Example 37 was conducted, except that modifiedpolyvinyl acetal resin PC1 was used in place of PB2. Thus, resincomposition CC1″″ was obtained, which was examined for dielectricconstant and dielectric loss tangent at 10 MHz in the same manner as inExample 37.

Example 40

The same procedure as in Example 37 was conducted, except that modifiedpolyvinyl acetal resin PD1 was used in place of PB2. Thus, resincomposition CD1″″ was obtained, which was examined for dielectricconstant and dielectric loss tangent at 10 MHz in the same manner as inExample 37.

Example 41

The same procedure as in Example 37 was conducted, except that modifiedpolyvinyl acetal resin PE1 was used in place of PB2. Thus, resincomposition CE1″″ was obtained, which was examined for dielectricconstant and dielectric loss tangent at 10 MHz in the same manner as inExample 37.

Comparative Example 14

In 24 g of methyl ethyl ketone were dissolved 16.0 g of an epoxy resin(Epikote 828, manufactured by Yuka Shell Epoxy K.K.) and 0.48 g of1-(2-cyanoethyl)-2-ethyl-4-methylimidazole to obtain resin compositionCX″″. This composition was applied to a Teflon sheet with an applicatorhaving a gap of 10 mils, and the coating was dried at 60° C. for 0.5hour and then heated in a hot-air drying oven at 180° C. for 2 hours tocure the resin.

The Teflon sheet was peeled-off, and the filmy resin obtained wasexamined for dielectric constant and dielectric loss tangent at 10 MHzusing an impedance analyzer (HP4291A, manufactured by HEWLETT-PACKARDCo.)

The results obtained in Examples 38 to 41 and Comparative Example 14 areshown in Table 9.

Table 9 shows that the cured compositions obtained from the resincompositions respectively containing modified polyvinyl acetal resinsPB2, PA2, PC1, PD1, and PE1, were lower in dielectric constant and/ordielectric loss tangent than the cured composition obtained from theresin composition containing none of these resins.

TABLE 9 Dielectric constants and dielectric loss tangents of epoxy resincontaining modified polyvinyl acetal resin Modified ε Curable Curingpolyvinyl (10 tan δ resin agent acetal resin MHz) (× 10E−3) Example 38Epikote 2E4MZCN modified 2.8 26.0 828 (1.2) (0.036) polyvinyl acetalresin PB2 (1.8) Example 39 Epikote 2E4MZCN modified 2.3 20.0 828 (1.2)(0.036) polyvinyl acetal resin PA2 (1.8) Example 40 Epikote 2E4MZCNmodified 2.6 24.5 828 (1.2) (0.036) polyvinyl acetal resin PC1 (1.8)Example 41 Epikote 2E4MZCN modified 2.3 20.3 828 (1.2) (0.036) polyvinylacetal resin PD1 (1.8) Example 42 Epikote 2E4MZCN modified 2.4 19.7 828(1.2) (0.036) polyvinyl acetal resin PE1 (1.8) Comparative Epikote2E4MZCN none 3.5 31.7 Example 14 828 (0.48) (16.0) Epikote 828 is anepoxy resin manufactured by Yuka Shell Epoxy K.K. 2E4MZCN is1-(2-cyanoethyl)-2-ethyl-4-methylimidazole. The numeral in eachparenthesis indicates the incorporation amount (g).

Epikote 828 is an epoxy resin manufactured by Yuka Shell Epoxy K.K.2E4MZCN is 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole. The numeral ineach parenthesis indicates the incorporation amount (g).

As described above in detail, the modified polyvinyl acetal resin havinga specific structure of the invention has a low dielectric constant anda small dielectric loss tangent and is excellent in compatibility withresins and adhesiveness to substrates.

Consequently, the resin of the invention is useful in applications whereelectrical insulating properties and mechanical properties areespecially required, such as, e.g., substrates for printed circuitboards and parts for computers. Substrates, electronic parts, and thelike each having excellent performances are obtained with the resin.

By using the modified polyvinyl acetal resin having a specific structureaccording to the invention, the film-forming ability of a curable resinis improved significantly and a resin composition is obtained whichgives a laminated product excellent in adhesiveness to the substrate andin flexibility.

Furthermore, by using the modified polyvinyl acetal resin having aspecific structure according to the invention, the film-forming abilityof a curable resin is improved significantly and a laminated productexcellent in adhesiveness to the substrate and in flexibility can beobtained.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A modified polyvinyl acetal resin consistingessentially of repeating units represented by the following formula (I):

wherein R¹ represents an optionally substituted aryl group, anoptionally substituted aralkyl group, or an optionally substitutedalkenyl group having an optionally substituted aryl group; R² representsa hydrogen atom or an alkyl group having 1 to 10 carbon atoms; R³represents an optionally substituted, bivalent hydrocarbon group having1 to 20 carbon atoms; and a, b, c, d, and e indicate the proportions inmol % of the respective structural units in the formula and satisfy0≦a≦85, 0≦b≦80, 0≦c≦50, 0≦d≦30, and 0<e≦50.
 2. The modified polyvinylacetal resin of claim 1, wherein a+b is from 30 to 80 mol %.
 3. Themodified polyvinyl acetal resin of claim 1, which is a modifiedpolyvinyl acetal resin obtained by acetalizing a polyvinyl alcohol withan aldehyde and then modifying the resultant acetalization product withan acid anhydride.
 4. The modified polyvinyl acetal resin of claim 2,which is a modified polyvinyl acetal resin obtained by acetalizing apolyvinyl alcohol with an aldehyde and then modifying the resultantacetalization product with an acid anhydride.
 5. The modified polyvinylacetal resin of claim 3, wherein the polyvinyl alcohol used as astarting material has a degree of polymerization of from 30 to 3,000. 6.The modified polyvinyl acetal resin of claim 4, wherein the polyvinylalcohol used as a starting material has a degree of polymerization offrom 30 to 3,000.
 7. A modifier for a curable resin, said modifiercomprising the modified polyvinyl acetal resin of claim
 1. 8. Themodifier of claim 7, wherein the curable resin is a resin for forming ananisotropic conductive film.
 9. The modifier of claim 7, wherein thecurable resin is a resin for forming an interlayer dielectric.